The programming interface

The programming interface in the fragment in Listing 3 consists of the prototypes for:

• A constructor that receives initialization parameters.
• An overloaded plus operator function, presumably allowing users of the class to add an integral number of days to the date (without seeing the full definition of the overloaded operator function, we can't be sure of its purpose).

The nomenclature you see in Listing 3 consists only of the prototypes of the member functions.

The definition of the member functions must be provided elsewhere.